The present invention generally relates to roller assemblies of the type adaptable for feeding sheet material such as paper, carton, foil and the like through a finishing plant. In particular, the present invention is directed to a novel vacuum roller assembly including a plurality of spaced suction ports formed therein, which are in fluid communication with a source of vacuum suction. The roller assembly further includes a resiliently deformable outer shell provided with a plurality of slit-like openings in fluid communication with the suction ports to provide a substantially uniform suction network over the roller surface to draw the sheet material into non-slip contact with the roller assembly.
Known vacuum roller assemblies have proven less than completely satisfactory in their inability to provide substantially uniform suction between the roller assembly and sheet material. As a result, the sheet material tends to slip relative to the rotating roller. A further disadvantage of known vacuum roller assemblies is their general inability to compensate for sheet material of varying thickness. As a result, the vacuum ports and fixed grooves formed on known roller assemblies will tend to leave undesirable tracks or markings on sheet material having a fine substratum. Because fixed grooves are employed in prior art assemblies, any dirt which may settle between the groove walls can be easily transferred to the surface of the sheet material.
As for example, U.S. Pat. No. 3,562,883 issued Feb. 16, 1971 to Koyabashi suggests a suction press roll including a plurality of fixed wall grooves extending across the roller surface into fluid communication with a plurality of separate suction ports. A vacuum is applied through the grooves to draw water from sheet material fed across the roller assembly. The fixed groove arrangement suggested in Kobayashi provides a substantially constant vacuum which may not be appropriate for sheet matter of widely varying composition. Furthermore, because of the fixed groove wall spacing suggested in Kobayashi, dirt and the like can easily accumulate within the grooves. Finally, because grooves of the type suggested in Kobayashi are generally machined into the roller body, the resulting production costs can be relatively high.
As will be discussed in detail hereafter, applicant's new and useful vacuum roller assembly solves the problems contronting prior art, while at the same time providing an inexpensive assembly wherein the deformable slit-like openings provide a variable suction force for drawing sheet material of varying thickness into non-slip contact with the foller assembly.